Exascale fabric time synchronization

Methods and apparatus for implementing time synchronization across exascale fabrics. A master clock node is coupled to a plurality of slave nodes via a fabric comprising a plurality of fabric switches and a plurality of fabric links, wherein each slave node is connected to the master clock node via a respective clock tree path that traverses at least one fabric switch. The fabric switches are configured to selectively forward master clock time data internally along paths with fixed latencies that bypass the switches' buffers and switch circuitry, which enables the entire clock tree paths to also have fixed latencies. The fixed latency of the clock tree path is determined for each slave node. The local clocks of the slave nodes are then synchronized with the master clock by using master clock time data received by each slave node and the fixed latency of the clock tree path from the master clock node to the slave node that is determined. Techniques for determining a clock rate mismatch between the master clock and a local clock is also provided.